A conventional BGA (Ball Grid Array) semiconductor package with a heat-dissipating device is illustrated in FIG. 5, as designated by the reference numeral 1. In the drawing, this semiconductor package 1 includes a substrate 10 having a first side 10A and a second side 10B, with a semiconductor chip 12 mounted on the first side 10A and electrically connected to the substrate 10 via gold wires 11. Further, a heat sink 13 is attached to the first side 10A of the substrate 10 by means of an adhesive 16. The heat sink 13 is composed of a flat section 130 and supporting sections 131 used to support the flat section 130 to be positioned above the chip 12 at a predetermined height. A receiving space 132 defined by the flat section 130, the supporting sections 131 and the first side 10A of the substrate 10 is used to receive the chip 12 and the gold wires 11 therein. Moreover, an encapsulant 14 is formed through a molding process to hermetically enclose the chip 12, the gold wires 11, the heat sink 13 and the first side 10A of the substrate 10, with an upper side 130A of the flat section 130 of the heat sink 13 exposed to the atmosphere. Finally, a plurality of solder balls 15 are mounted on the second side 10B of the substrate 10.
One drawback to the foregoing BGA semiconductor package 1, however, is that the heat sink 13 may be attached to the substrate 10 in a slant manner, due to failure in accurately controlling the amount of the adhesive 16 applied to the supporting sections 131, as shown in FIG. 5. As a result, a portion 130C of the flat section 130 slants downwardly and a spacing is then formed between an encapsulating mold (not shown) for forming the encapsulant 14 and the portion 130C during the molding process, allowing flash of a molding resin used for making the encapsulant 14 to form on the portion 130C; when the upper side 130A of the flat section 130 of the heat sink 13 for heat-dissipation is partly covered by the flash of the molding resin, the area of the upper side 130A directly exposed to the atmosphere is decreased and the heat-dissipating efficiency thereof is reduced. Accordingly, another portion 130D of the flat section 130 is upwardly slanted in response to the downward slant of the portion 130C, which leads to damage to the substrate 10 resulting from the clamping force generated by the encapsulating mold for forming the encapsulant 14. Therefore, quality and appearance of the semiconductor package 1 are degraded.
Another drawback to the aforementioned semiconductor package 1 is that, the heat sink 13 can not be positioned precisely on the substrate 10 by using the adhesive 16 for attachment thereof. If the heat sink 13 is not disposed in a predetermined position, the package appearance may be damaged, and short circuit may occur, due to accidental contact of the supporting section 131 with the gold wires 11 used for electrically connecting the chip 12 to the substrate 10.
In conclusion, it is disadvantageous to manufacture a semiconductor package with planarity and positioning of a heat sink mounted therein unable to be assured, and it is also cost-ineffective and a waste of resources to discard those unqualified products. In addition, a complex process, e.g. stamping, is required for the manufacture of the heat sink with the desired flat section and supporting sections, and thus the manufacturing cost is increased.
It is therefore an objective of the present invention to provide a semiconductor package with a heat-dissipating structure and the method for making the same, which assure the planarity and positioning of the heat-dissipating structure on a substrate on which the heat-dissipating structure is mounted so as to enhance the quality and yield of the manufactured package and to lower the manufacturing cost.
It is another objective of the invention to provide a semiconductor package with a heat-dissipating structure and the method for making the same, which simplify the manufacturing process and reduce the manufacturing cost thereof, due to the attachment of the heat dissipating structure to the substrate being free of the use of any adhesive.
It is still another objective of the invention to provide a semiconductor package with a heat-dissipating structure and the method for making the same, which help prevent flash from contaminating the surface of the heat-dissipating structure exposed to the atmosphere.
It is yet another objective of the invention to provide a semiconductor package with a heat-dissipating structure and the method for making the same, which help increase the heat-dissipating efficiency by forming a protrusion on the heat-dissipating structure toward the semiconductor chip.
In accordance with the foregoing and other objectives of the invention, a semiconductor package with a heat-dissipating structure and the method for making the same are proposed. The semiconductor package of the invention includes a substrate having a first side and a second side; a semiconductor chip attached to and electrically connected to the first side of the substrate; a heat-dissipating structure comprising a heat sink having a first surface and a second surface and a plurality of solder columns attached to the second surface of the heat sink, so that the heat sink is elevated to a predetermined height above the semiconductor chip via the solder columns when the heat-dissipating structure is mounted on the first side of the substrate via the solder columns; an encapsulant formed on the first side of the substrate so as to encapsulate the semiconductor chip and the heat-dissipating structure in a manner that the first surface of the heat sink is exposed to the exterior of the encapsulant; and a plurality of conductive elements attached to the second side of the substrate.
The method for making the semiconductor package of the invention comprises the steps of: providing a heat sink having a first surface and a second surface; forming a plurality of concaves at preset positions on the second surface of the heat sink, the concaves being arranged in position not to interfere with electrical connection between a semiconductor chip and a substrate for carrying the semiconductor chip and the heat sink; attaching a plurality of solder columns to the concaves on the second surface of the heat sink respectively to form a heat-dissipating structure; providing a substrate having a first side and a second side; forming on the first side of the substrate a plurality of connecting pads for attaching the solder columns; mounting at least one semiconductor chip on the first side of the substrate and electrically connecting the semiconductor chip to the substrate; attaching the heat-dissipating structure to the first side of the substrate by reflowing the solder columns to the connecting pads on the substrate; forming an encapsulant on the first side of the substrate to encapsulate the semiconductor chip and the heat-dissipating structure, while allowing the first side of the heat sink to be exposed to the atmosphere; and mounting a plurality of conductive elements on the second side of the substrate.
Alternatively, the manufacture of the semiconductor package of the invention may further comprise a step of encapsulating the semiconductor chip mounted on the substrate, prior to the step of attaching the heat-dissipating structure to the substrate by reflowing the solder columns to the connecting pads of the substrate.
The concaves on the second surface of the heat sink may be formed by etching solder mask coated on the heat sink.
The solder columns are made of material having a melting point lower than that of the heat sink, such that the solder columns are flexible in nature and capable of acting as a cushion between the heat sink and the substrate to thereby prevent the substrate from being damaged during a molding process for forming the encapsulant. The material suitable for the solder columns may be the one selected from the group consisting of tin, lead, and tin/lead alloy.
Further, the heat sink can be further formed with a protrusion from the second surface thereof toward the semiconductor chip mounted on the substrate. By this arrangement, the heat-dissipation efficiency of the semiconductor package of this invention can be further enhanced due to the decreased distance between the heat sink and the semiconductor chip.